Fluid circulation chambers generally include an inlet fluid distributor grating and an outlet fluid collector grating. The inlet grating is intended to deflect the flow and to decelerate the fluid, while the outlet grating is intended to deflect the flow and to accelerate the fluid, the idea being to obtain uniform fluid velocity between the gratings.
In conventional chambers of this type, the inlet and/or outlet gratings are constituted by thin, plane, perforated metal sheets which are generally associated with inlet and outlet passages of constant height. Since the thinly-edged perforations through these grids have no effect on the tangential components of the inlet air velocity, large oblique velocity components remain inside the chamber in spite of the spreading out effect of the inlet grating. These high velocity components, combined with the effect of the walls of the chamber, leave the air un-evenly spread out inside the chamber.
A system for correcting inlet flow may be improved by creating a flow deflecting effect using a thick perforated sheet, such that the ratio of the sheet thickness to the diameter of the perforations is high, and in any case greater than five. Any fluid entering such perforations obliquely tends to stick to the walls thereof and thus leaves flowing along a direction substantially perpendicular to the plane of the sheet. This arrangement suffers from the drawback of either requiring sheets that are thick, heavy and expensive, or else requiring medium thickness sheets that are perforated by very small holes which tend to become clogged with any solid particles that may be in suspension in drying air, for example.
Another way of improving flow correction that is sometimes successful is to use a honey-comb panel of sufficient thickness to deflect the flow appreciably. Nonetheless, a honey-comb has the disadvantage of head loss that is low, and highly variable depending on the angle of incidence of the fluid on its inlet side. Honey-combs are thus primarily used in situations where the fluid to be deflected is is itself applied to the panel at a speed and along a direction that are both uniform and regular. This can require the addition of a perforated sheet to provide improved spreading out of the fluid at the cost of extra average head loss. An additional drawback is that glued honey-combs are useable only at fairly low temperatures.
Likewise, at the outlet from the chamber, a large suction pressure difference must be created along the outlet passage to enable the air to leave it rapidly in a direction which is generally perpendicular to the plane of the outlet sheet. This pressure difference further upsets the uniformity of flow through the chamber. One way of combatting the effects of the suction pressure difference required along the outlet passage is to use an outlet grating that causes a head loss which is large in comparison with the suction pressure difference. This leads to the use of sheets with excessive head losses giving mediocre results even when used in conjunction with divergent passages.
Preferred embodiments of the invention provide gratings which ensure adequate uniformity in the flow of fluid downstream from an inlet grating and/or upstream from an outlet grating. This is done simply and without excessive head loss.